Cole Hamels versus Zack Greinke

Getty Images/AP PhotoCole Hamels and Zack Greinke have similar contracts and peripherals, but not the same ERAs.

Last summer, Cole Hamels signed a six-year $144 million contract to remain with the Philadelphia Phillies through 2018. Just a few weeks ago, Zack Greinke signed a six-year, $147 million contract with the Los Angeles Dodgers. Over the past three seasons, Greinke has a 3.17 xFIP while Hamels is a sliver worse at 3.18. These are two very similar pitchers, or so you’d think.

Since 2010, Hamels has outpitched Greinke ERA-wise by nearly a full run, 2.95 to 3.83. This is despite the two just about matching each other in strikeout rate (Hamels 24.2 percent, Greinke 23.3 percent), walk rate (6.1 percent, 6.2 percent) and ground ball rate (46.9 percent, 47.4 percent). How can two virtually identical pitchers have such a massive disparity in ERA?

DefenseAs Yuniesky Betancourt's presence may have indicated, the Royals put together some lousy defenses during Greinke's tenure in Kansas City. According to defensive efficiency, a stat found at Baseball Prospectus, the Royals were the worst defensive team in 2004 and '05, and were close to the bottom in 2007, '09 and '10. And while the Phillies have never been an elite defensive club in recent years, they have been closer to the middle than the bottom, finishing in the top five in the National League in '08, '10 and '11.

Ultimate zone rating, a defensive stat found at FanGraphs, paints an even better picture for the Phillies. In each of Hamels' seasons, the Phillies finished in the top 10 in the NL, while Greinke's Royals finished in the bottom three in the AL four times. In Greinke's six seasons in Kansas City, the Royals were 134 runs below average (average minus-22 runs per season) while the Phillies were 95 runs above average in Hamels' seven seasons (average plus-14 runs per season).

As Hamels himself learned in 2009, sometimes your own success and failure is out of your control. A run of bad dice rolls can add up quickly and create some funny-looking numbers. In this case, the various amalgamations of defenses created by the Royals hurt Greinke and the rest of their pitchers more than they likely realized. The Phillies have had plus defenders at catcher, second base, shortstop, third base, center field and right field for most of Hamels' career.

Designated hitterThis reason is fairly intuitive. Hamels has benefited greatly from a reprieve at the bottom of the lineup while Greinke has had to face a bona fide hitter in the DH spot throughout most of his career. Since 2004, the average DH in the American League posted a wOBA between .333 and .352. During Hamels' career, the average pitcher in the National League posted a wOBA between .150 and .167.

Which pitcher would you most want for 2013?

30%

Zack Greinke

70%

Cole Hamels

(Total votes: 3,239)

Not only is it easier to face the pitcher, but the No. 8 hitter can be avoided if necessary as well. Last season, NL No. 8 hitters were intentionally walked 174 times in 10,010 plate appearances (1.7 percent) while AL No. 8 hitters were given the intentional pass only 41 times in 8,850 plate appearances (0.5 percent).

Pitcher BABIPOne of the most important Sabermetric findings came from Voros McCracken, who discovered that pitchers, for the most part, have very little control on the rate at which batted balls are converted into outs. Since then, we have refined that theory except to pitchers at the extreme ends of the BABIP spectrum (such as Jeremy Hellickson), but it is still by and large fairly accurate.

Over larger samples, though, individual batted ball skill starts to shine through. In 1,376.2 regular-season innings, Hamels has an overall .282 BABIP. In 1,492 regular-season innings, Greinke has an overall .308 BABIP. With both pitchers having induced somewhere in the neighborhood of 4,000 batted balls over their careers, the 26-point difference is about 104 hits in total. According to FanGraphs, the run value of a single relative to an out is 0.89 runs, so the difference is about 93 runs if you assume the least, that all of those extra hits were singles. Some of the BABIP disparity comes from the aforementioned defenses, so the 26-point gap isn't just the pitchers. It is very difficult to untangle the two.

There is a vast disparity between Hamels and Greinke when runners are in scoring position. According to play-by-play data dating back to 2009, Hamels has a .283 BABIP and .282 wOBA with RISP, while Greinke has a .337 BABIP and .314 wOBA. As a result, Greinke's strand rate is 5.6 percent lower. In other words, for every 20 runners who reach base, Greinke has allowed one extra runner to score compared to Hamels. Since 2009, both pitchers have faced roughly 3,500 batters and allowed just more than 1,000 of them to reach base, so the 5.6 percent gap in strand rate amounts to about 50 runs.

Is Hamels really as good -- and Greinke really as bad -- as ERA indicates? It doesn't appear to be the case in a vacuum. If you put both pitchers in the same league facing the same hitters with the same defense behind them, they would likely put up remarkably similar numbers. Now with the Dodgers, though, Greinke will have a defense that is sufficiently average according to ultimate zone rating, and he will benefit from the pitcher-friendly confines of Dodger Stadium. Perhaps 2013 is the year Greinke returns to his Cy Young-caliber ways.

Bill Baer runs the Phillies blog Crashburn Alley. You can follow him on Twitter @CrashburnAlley.